Separation of uranium isotopes by chemical exchange

ABSTRACT

A chemical exchange method is provided for separating uranium235 from uranium-238 comprising contacting a first phase containing UF6 with a second phase containing a compound selected from the group consisting of NOUF6, NOUF7, and NO2UF7 until the UF6 in the first phase becomes enriched in the U-235 isotope.

United States Patent [191 Ogle, Jr.

[451 Feb. 26, 1974 SEPARATION OF URANIUM ISOTOPES BY CHEMICAL EXCHANGE[75] Inventor: Pearl R. Ogle, Ji'., Westerville, Ohio [73] Assignee: TheUnited States of America as represented by the United States AtomicEnergy Commission, Washington, D.C.

[22] Filed: Sept. 13, 1972 [21] Appl. N0.: 288,860

521 US. Cl 423/253, 423/258, 252/301.1 R 51 Int. Cl C0lg 43/00 58 Fieldof Search 423/253, 258; 252/301.1 R

[56] References Cited UNITED STATES PATENTS 3,697,235 10/1972 Ogle..423/253X 3,039,846 6/1962 Ogle 423/253 Primary Examiner-Carl D.Quarforth Assistant Examiner-R. L. Tate Attorney, Agent, or FirmRolandA. Anderson; John A. Horan; Irving Barrack [57] ABSTRACT 12 Claims, 2Drawing Figures SEPARATION OF URANIUM ISOTOPES BY CHEMICAL EXCHANGEBACKGROUND OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING In thedrawing FIG. 1 is a diagramatic representation of a system for carryingout this isotopic exchange process, and

FIG. 2 presents details of a portion of the system for monitoring itsoperation.

DESCRIPTION OF THE INVENTION The present invention is based on thediscovery that, when a first phase containing a UF complex compoundrepresented by the general formula M,,,(UF,,), alone or dissolved in' afluoride-containing solvent is contacted with a second phase immisciblewith said first phase and containing gaseous or liquid UF alone ordissolved in a perhalogenated solvent, the UF phase will become enrichedin the urahiurh-mrsoro s. M represents a univ'alent positive metal ionor radical which is associated with the UF,,"" or uranium-bearingcomplex fluoride anion of charge 111. In general, the number n offluoride ions F and the valence state of the uranium atom will determinethe charge In and hence the formula of the resulting UF complex salt.Examples of compounds represented by M,,,(UF,,) include NOUF (M N, n 6,m I),NOUF (M= N0 n 7, m l), and NO UF (M=NO n=7, m= 1). Thus, when afirst phase containing a solid compound selected from the groupconsisting essentially of NOUF NOUF and NO UF alone or dissolved in afluoride-ion-containing solvent is contacted with a second phasecontaining gaseous or liquid UF alone or dissolved in a perhalogenatedsolvent, the second UF containing phase will become enriched in theuranium- 235 isotope. In order to achieve enrichmenut he two phasesundergoing isotopic exchange must satisfy certain basic requirementswhich are delineated below.

1. The two phases must be stable, not only with respect to each otherbut the substances used in contacting them. In that sense, the presentinvention can be represented by the following two-phase systems which Ihave found to undergo isotopic exchange and which are compatibleandseparable without adverse chemical reaction.

First Phase Second Phase A. NOUF (s) :UF,; (1) or (g) B. NOUF (s) :UF(l) or (g) C. NO UF (s) :UF,, (1) or (g) D. NOUF (s) :UF, 1) or (g)I-IF(g) E. NOUF in HF :UF in perfluorotributylamine (FC- F. NOUF in,HFzUF in trichlorotrifluoroethane (F- 2 NOUF in HFzUF indichlorotetrafluoroethane (F-1l4) H. UF6 in HF:UF6 in FC-43 I. UFG inHFzUF in F-l 14 where (s) solid, (1) liquid, and (g) gas.

2. The equilibrium constant established between the two phases of A-I,inclusive, is greater than unity where the equilibrium constant, orsingle stage separation factor, a, is defined as a[U-23Sl/IU-ZSBll/IUQiSI/IU-Zifi where I [U-2351/[U-23 816 the uraniumf35-To -uranium- 238 mole ratio in the U-235 enriched phase, and[U-2351/[U-238L1 the uranium-235-to-uranium- 238 mole ratio in the U-235depleted phase. Isotopic concentrations were obtained by massspectrometry using the standard technique described in "HD7029, aEubTicaEon tiffi U. S. AtomTcErTer'gy 1 Commission entitled SelectedMeasurement Methods for Plutonium and Uranium in the Nuclear Fuel Cycleby R. J. Jones (1963).

Isotopic exchange to give an a greater than unity occurs in each ofreactions A-I, inclusive, but the greatest value was found to occurbetween the uranium compounds NOUF UF Thus, systems A, D, E, F, and Ginvolve the same exchange reaction; i.e.,

U F NOU F U F NOU F Wham o fis'ufiah'rriehraeeurgEnem 3. The rate ofisotopic exchange must be very rapid since this rate determines the timerequired to reach equilibrium. System A was studied by varioustemperatures. Known amounts of the two components were added to a nickelreactor and left at a designated temperature for a desired length oftime. The reactor was then quickly cooled to room temperature in orderto freeze the exchange reaction and a portion of the UP was removed formass, spectrometer analysis. The amount of UF removed from the reactorwas noted and a new UF /NOUF mole ratio was determined. The procedurewas repeated at several temperatures and the results for runs attemperatures in the range 25 to 190 C. are shown in Table I.

TABLE I Determination of Single Stage Uranium Isotopic SeparationFactors for the System: U F (g,l) NOU F (s) U F (g,l) 2as s( at VariousTemperatures I Temp., Contact Time Mole Ratio 11 C. UFSINOUFB 25 7 days0.853 1.00002 13 days 0.747 1.00010 37 days 0.571 0.99998 79 days 0.41310.99998 120 days 0.390 1.00000 2 hours 0.682 1.00000 4 hours 0.9241.00000 21 hours 0.668 1.000l7 64 hours 0.595 l.0005l 64 hours 1.0571.00053 64 hours 3.57l l.00073 2 hours 0.914 1.00000 4 hours 1.0531.00000 4 hours 1.311 1.00000 8 hours 0.834 1.00000 16 hours 0.7951.00000 16 hours 2.345 1.00000 64 hours 0.846 1.00037 64 hours 0.0541.00046 120 hours 0.356 120 hours 0.028 1.00076 144 hours 0.062 1.00079153 16 hours 1.156 1.00045 16 hours 0.0007 1.00042 16 hours 2.2641.00000 24 hours 0.882 1.00030 80 hours 0.086 1.00068 88 hours 0.7301.00033 130 hours 0.077 1.00065 226 hours 0067 1.00069 232 hours 06811.00029 190 16 hours 0437 1.00030 33 hours 0.34) 1.00042 81 hours 0.2921.00063 225 hours 0257 1.00047 TABLE 11 Single Stage Separation Factor(01) for the System: NOUF (s):UF (g):HF(g) At 25C. Mole Ratio, ContactTime, NoUF zUF zHF a 4 solvent immiscible with and having an appreciablydifferent density than the solvent for NOUF in order to cascade thesingle stage operation. Systems E-l, inclusive, are examples ofliquid-liquid reversible chemical exchange between the designatedphases. Thus, when the four components NOUF HF, UF and any one of thedesignated fluorocarbons are mixed, two phases result which areimmiscible. The heavy phase (H.P,) is predominantly fluorocarbon and UFwhile the light phase (L.P.) is predominantly hydrogen fluoride and NOUFSystem E was used to determine that the equilibrium concentration forreaction, as represented by the preceding equation, was establishedwithin a few minutes. System G was used to cascade the single stageenrichment by flowing the heavy phase downwardly in dropwise fashionthrough a static column of N OUF, in

HF.F-l 14 is the preferred fluorocarbon because of the greatersolubility of UF in that solvent. Table 111 below presents the UFdistribution coefficient (DC) for system G.

TABLE III Distribution Coefficient of UF Between Freon-114 (Heavy Phase)and Liquid HF (Light Phase) Distribution Coefflcient Liquid HF Freon-114Liquid HF *The weight ratios of NOUF IHF in the five tests were between0.70 and 0.77.

0.5 1107923012479 1.00094 2 .02687:1 1.00 2 I 3 321,; 52 Systems H and lwere used to determme the d1str1bu- 2 11099587163941 100088 tlon of UFbetween the fluorocarbon and HF and the :3 lf'gggggg'gl 188838 degree ofisotopic enrichment. The data obtained for 190 l:2.73787:8.02 1.00090system H are summarized in Table IV below.

QTAMTV V 7 TABLE IV V 7 Distribution Data of System H at 25 C.

Cone. UFB (H.P.) Mole fraction G. UFU/ G. 11 Cone. UF6 (L.P.) UF ITO-43HF g. .P. g HP. 01

240 1-1 20378-10180 100076 240 H) 820161175 {00m The data show ennchmentoccurred In the heavy 312 jj j 1:000 (fluorocarbon) phase. The values ofa for system 1 av- 450 109 ;917:7025 1.00118 eraged only 1.00007.

It will be noted that the addition of hydrogen fluoride to the UF -NOUE,mixture produced exchange at 25 C. The magnitude of the exchange wasnearly as large in 0.5 hour as at the end of 456 hours, indicating thatthe presence of HF materially reduced the time necessary to establishthe equilibrium concentration. Hydrogen fluoride was found to exhibitsimilar effects on the other listed UF -NOUF systems but had no effecton systems B and C.

Cascading Effect The Best Mode The best mode of practicing thisinvention is by counter-currently contacting the UF phase and a NOUFphase in'a column between a first liquid phase containing NOUF dissolvedin a suitable solvent that is stable toward and does not appreciablydissolve UF and a second liquid phase of UF, dissolved in a stable inertRepresentative Embodiment of Best Mode System G (NOUF in HF and UP inF-] 14) was used to operate an isotopic exchange process in thecountercurrent contact mode. The contacting equipment, as shown in FIG.1, comprised a column made of onefourth-inch schedule 40 monel pipe 10with a contact length of about 17 feet with a side arm 12 near the topend of the pipe. The bottom end of the pipe and the side arm terminatedin fluorethene receivers 14 and 16 for emptying the contacted heavy andlight phases, respectively. Feed cylinders 18 and 20 served as sourcesfor the light phase and heavy phase, respectively. The equipmentincluded associated piping valves, unnumbered, and pressure gauges 19,21, and 23 as shown in FIG. 1. Sight glass bodies 22 and 24 were weldedinto the column 10 to permit observance of fluid flow.

Lights behind the translucent fluorethene receivers permit visibility ofliquid levels. Visibility was enhanced because the blue-green color ofthe light phase contrasted sharply with the water-clear heavy phase. To-

operate the equipment, column was first filled with the light phasematerial through the light phase feed line to a level just below theside arm 12. Heavy phase material was added in discrete droplets from atube 26 submerged beneath the surface of the light phase liquid. Asshown more clearly in FIG. 2, the end of the tube was located at sightglass 22 so that droplet formation and rate of addition could bemonitored. As the heavy phase was added, it displaced an equal volume oflight phase material from column 10 into side arm 12. When the desiredquantity of heavy phase material was dropped through the light phase, itwas discharged to the heavy phase receiver 14. Both receivers werefrozen and removed and replaced by fresh receivers. Finally, fresh lightphase liquid was introduced into column 10 so that it was raised to itsoriginal level at the side arm, and the system was ready for the nextrun.

Heavy phase and light phase feed solutions were made from the samesource of UP so that they both initially had the same isotopicconcentration. A total of 25 runs were made in the manner described andanalyzed for isotopic concentration.

The isotopic analysis was made by comparing the ratio of isotopes in thesample to the ratio of isotopes in the original material (which was usedas a standard) on a mass spectrometer to ascertain a ratio R,whereR=CU-235/U-238 (of sample)/U-23 5/U-238 (of standard). Enrichment in theUifiiscfipe is fridicatdby flame of R greater than 1', depletion in theU-235 isotope by a ratio less than 1, and no enrichment or depletion bya ratio of 1 It was foun dth attlie U fiii sotope con centrated in theheavy phase. A summary of analytical results for selected runs is givenin Table V.

TABLE V Analytical Results of Initial Column Operation at 25C.

[U-235/U-238 (sample)]/[ U-235/U-238 -(standard)] Run Heavy Phase LightPhase Heavy to Light No. Ratio Ratio Phase Ratio 2 1.00113 0.999991.00113 5 1.00118 0.99992 1.00126 10 1.00108 0.99966 1.00142 0.999381.00211 1.00180 Actual contact of the heavy and light phases was on theorder of seconds, indicating rapid attainment of enrichment.

Column Operation with Reflux phase occurs by adding 35 to 50 percentexcess NO to the contacted heavy phase and heating with agitation at atemperature in the range 25 to C. After cooling, the Freon-114 (F-l 14)and excess NO is pumped off, HF added to the NOUF and mixed sufficientlyto effect-solution of the HF. The resulting solution now servesas a newfeed supply for a succeeding cycle of operation. Thus, the new feedmaterial contained the converted heavy phase material from the previouscycle.

Conversion of the NOUF -containing light phase is accomplished byaddition of F or ClF to the NOUF HF mixture at a temperature in therange 25 to 40 C. Of the two fluorinating agents,'ClF is preferred and,when used, requires a ClF /NOUF mole ratio of at least 2 to obtain goodconversion. The NOUF dissolved in HF produces a blue-green solutionwhich turns to a light yellow to colorless solution upon addition ofeither fluorinating agent. The UF is then recovered by extraction man-n3 F-TIZI or F C-43 to form a new heavy phase for recycling back to thecolumn.

Thus we have described a chemical exchange process with interconversionof each species to the other as it issues from the exchange region.

What is claimed is:

method f or separating uranium-2 35 from uranium-238 comprisingcontacting a first gaseous or liquid phase containing UF with a secondliquid or solid phase containing a compound selected from the groupconsisting of NOUF NOUF and NO UF until the U F in the firstphasebecomes 65176553761112: D 235 isotope. y

2. The method according to claim 1 wherein the first and second phasesare selected from the group consisting of First Phase Second Phase A.NOUF (s) :UF.; (1) or (g) B. NOUF (s) :UF (l) or (g) C. NO UF (s) :UF(1).or (g) D. NOUF '(s) :UF (1) or (g) HF(g) E. NOUF in HF :UF inperfluorotributylamine F. NOUF in HFzUF in trichlorotrifluoroethane G.NOUF in HFzUF in dichlorotetrafluoroethane wherels) solid, (1) liquid,and (g) f gas.

3. A method for separating U-235 and U-238 which comprisescountercurrently contacting a first liquid phase consisting essentiallyof UF dissolved in a liquid fluorinated hydrocarbon which is essentiallyimmiscible with HF and a second phase consisting essentially of NOUFdissolved in HF until the UF becomes enrichedfin th e TT-Qiisbtdfi.

4. The method according to claim 3 in which the solvent for UP isselected from the group consisting of trichlorotrifluoroethane,dichlorotetrafluoroethane, and perfluorotributylamine.

STA met'hodof sesaraifilgn z'ssrrsm IT-2T8 comprising countercurrentlycontacting a first liquid phase consisting essentially of UP dissolvedin an essentially l-lF-immiscible liquid fluorinated hydrocarbon with asecond phase having a lower specific gravity than said first phase andconsisting essentially of NOUF dissolved in HF until the UF becomesenriched in the 6. The method according to claim 5 in which droplets ofthe heavier phase are passed through a column containing the lighterphase.

7. The method according to claim in which droplets of the heavier phaseare passed through a column filled with the lighter phase to displacethe lighter phase in said column.

8. The method according to claim 5 in which the HF- immiscible solventfor UF is a fluorinated hydrocarbon.

9. A method of separating U-2 35 from U-238 comprising countercurrentlycontacting a first liquid phase consisting essentially of UF dissolvedin an essentially HF-immiscible liquid florinated hydrocarbon with asecond phase having a lower specific gravity than said first phase andconsisting essentially of NOUF dissolved in HF until the UP becomesenriched in the U-235 isotope, reacting the contacted TNOUWFI; with E orClF to form UP and cycling back the thus produced UR to serve as solutefor the first liquid phase.

10. The process according to claim 9 in which UP previously enriched inU-235 is reacted with NO to form NOUF to serve as solute for the secondliquid phase.

11. The method according to claim 9 in which the contacted NOUF phase,after disengagement from the UF -containing phase, is reacted with afluorinating agent selected from the group consisting of F or ClF toproduce UF to serve as solute for the first liquid phase.

12. The method according to claim 10 in which UF previously enriched inU-TS is disengaged from the lighter phase and reacted with NO to produceNOUF separating the resulting NOUF and reconstituting it with HF toserve as the second liquid phase.

2. The method according to claim 1 wherein the first and second phasesare selected from the group consisting of First Phase Second Phase A.NOUF6(s) :UF6 (1) or (g) B. NOUF7(s) :UF6 (1) or (g) C. NO2UF7(s) :UF6(1) or (g) D. NOUF6(s) :UF6 (1) or (g) - HF(g) E. NOUF6 in HF:UF6 inperfluorotributylamine F. NOUF6 in HF:UF6 in trichlorotrifluoroethane G.NOUF6 in HF:UF6 in dichlorotetrafluoroethane where (s) solid, (1)liquid, and (g) gas.
 3. A method for separating U-235 and U-238 whichcomprises countercurrently contacting a first liquid phase consistingessentially of UF6 dissolved in a liquid fluorinated hydrocarbon whichis essentially immisciblE with HF and a second phase consistingessentially of NOUF6 dissolved in HF until the UF6 becomes enriched inthe U-235 isotope.
 4. The method according to claim 3 in which thesolvent for UF6 is selected from the group consisting oftrichlorotrifluoroethane, dichlorotetrafluoroethane, andperfluorotributylamine.
 5. A method of separating U-235 from U-238comprising countercurrently contacting a first liquid phase consistingessentially of UF6 dissolved in an essentially HF-immiscible liquidfluorinated hydrocarbon with a second phase having a lower specificgravity than said first phase and consisting essentially of NOUF6dissolved in HF until the UF6 becomes enriched in the U-235 isotope. 6.The method according to claim 5 in which droplets of the heavier phaseare passed through a column containing the lighter phase.
 7. The methodaccording to claim 5 in which droplets of the heavier phase are passedthrough a column filled with the lighter phase to displace the lighterphase in said column.
 8. The method according to claim 5 in which theHF-immiscible solvent for UF6 is a fluorinated hydrocarbon.
 9. A methodof separating U-235 from U-238 comprising countercurrently contacting afirst liquid phase consisting essentially of UF6 dissolved in anessentially HF-immiscible liquid florinated hydrocarbon with a secondphase having a lower specific gravity than said first phase andconsisting essentially of NOUF6 dissolved in HF until the UF6 becomesenriched in the U-235 isotope, reacting the contacted NOUF6 with F2 orClF3 to form UF6 and cycling back the thus produced UF6 to serve assolute for the first liquid phase.
 10. The process according to claim 9in which UF6 previously enriched in U-235 is reacted with NO to formNOUF6 to serve as solute for the second liquid phase.
 11. The methodaccording to claim 9 in which the contacted NOUF6 phase, afterdisengagement from the UF6-containing phase, is reacted with afluorinating agent selected from the group consisting of F2 or ClF3 toproduce UF6 to serve as solute for the first liquid phase.
 12. Themethod according to claim 10 in which UF6 previously enriched in U-235is disengaged from the lighter phase and reacted with NO to produceNOUF6, separating the resulting NOUF6 and reconstituting it with HF toserve as the second liquid phase.